1. Field of the Invention
The present invention relates to the trade of shipbuilding and more specifically, to tubular shafts used in marine line shaftings.
The proposed invention is useful in propulsion and tunnel shafts of a ship's line shafting.
The present invention is also applicable in machine building and mechanical engineering practice, whenever it becomes necessary to impart high torque from the drive to the actuator mechanism using low weight line shafting.
2. Description of the Prior Art
It is known to use hollow (tubular) shafts for marine line shaftings, made of a solid forged piece by drilling out the centre (core) thereof. The disadvantage inherent in such a construction is the high labour consumption of the shaft production process and low material utilization factor.
It is also known to use tubular shafts made as a tube with tailpieces or extensions welded thereto, such as flanges or tapered extensions for setting the propeller screw and clutch member thereon. The disadvantage said shafts suffer from resides in their inability to impart high torque this being due to the fact that the present day level of production engineering can afford neither rolling nor drawing a tube of the required size and strength.
Known in the trade are prior-art shafts of marine line shaftings, made a multiple-layer shell built up of coaxially arranged tubes differing in diameter and length.
To unite the tubes into an integral structure the shaft has endpieces or extensions provided with stepwise annular recesses made to suit the diameter of each tube.
The endpieces of the tubes are taper-turned so as to fit into the respectively profiled annular recesses of the shaft extension. In addition, the shaft extension has an interior stepped chamber adapted to be closed by a threaded plug. Once the shaft has been assembled with the tubes, the interior stepped chambers in the shaft extentions are filled with asphalt compound urged under pressure developed by a thrust screw turnable into the threaded plug. It is under the pressure exerted that the walls of the shaft extension are deformed, thus establishing a tight fit of the tube ends in the recesses of the shaft extension. To minimize torsional vibrations, the intertube gaps are filled with an elastic silicone resin.
However, a simultaneous press-fitting of the tube ends by virtue of the pressure built up in the shaft extension precludes one from consecutively checking the end of each tube for quality of securing, whereby the whole structure cannot be regarded as reliable.
Moreover, provision of an interior chamber in the shaft extension is found to be difficult in cases where the propulsion shaft is to terminate in a tapered extension to fit the propeller screw thereon.
One more type of shaft used in marine line shafting is known to comprise coaxially arranged tubes of different diameter and length fitted over the shaft extensions and welded thereto.
In this case the shaft extensions have cylindrical stepwise recesses made to suit the tube bore diameter. The tubes are welded to the shaft extensions in succession, i.e., first the inner tubes, then the outer ones. To render the tubes weldable to the other shaft extension after the inner tube has been welded thereto, each of the outer tubes is consecutively extended by welding two-half inserts thereto.
To minimize torsional vibrations the intertube space is filled with silicone resin or plastics.
The disadvantage of said shafts resides in a multitude of weld joints which involve successive checkup and heat treatment to relieve stresses. Furthermore, filling of the interior spaces with cold-cure plastics or with resin following the welding of the outside tubes is impeded, while gradual filling of the spaces is precluded by heating due to welding and heat treatment of the outside tubes.
Moreover, torque-developed tangential stresses being distributed in direct proportion to the length of radius, a majority of torsional load stresses developed in the tubular shafts are taken up by the outer tubes, while the inner ones remain underloaded which results in an increased quantity of tubes used, larger mass of the shaft and higher labour consumption for its manufacture.
There are likewise known tubular shafts composed of a number of coaxial tubes, of which inner ones are to take up an additional torque load. This is attained as follows.
The endpieces of the coaxially arranged tubes carry disks spaced somewhat apart from the tube butt end and welded thereto, said disks having involute teeth with the same pitch circle diameter. Each of the outer tubes with its butt end thrusts against the disks welded to the inner tube which prevents axial displacement of the shorter outer tubes with respect to the inner ones. The involute teeth of the disks differ in thickness, i.e., the maximum-thickness teeth are in the disk welded to the innermost tube, while the disk welded to each of the next outer tubes has thinner teeth than the disk welded to the preceding inner tube.
Fitted onto the shaft extensions are clutches with internal involute toothing featuring the same thickness over the entire clutch length and adapted to get in mesh with the teeth of the disks welded to the tubes. The clutches are held in position on the outermost tube by nuts. One of the clutches has a flange for a conventional joining with the propulsion shaft or with the flange of the drive shaft. The other clutch engages the teeth of the disks welded to the tubes of the next tubular shaft. The intertube space is filled with an elastic silicone resin which adheres firmly to the tube surface.
The shaft of the character set forth above functions as follows. Owing to the fact that the teeth of the disks welded to the inner tubes are thicker than those of the disks welded to the outer tubes, it is the former teeth that are the first to take up torsional load. As soon as the innermost tube has been twisted to an angle corresponding to the clearance in the clutch engagement with the next disks, the load is taken by the next outer tube. Upon further twisting the load is taken up by the further outer tube so that at a rated torque all tubes are loaded nearly uniformly.
The disadvantage of the afore-described shaft construction resides in an inadequate rigidity of the shaft operating under variable load conditions, and especially under torsional vibrations, as well as in rendering the outer tubes beyond taking up torsional load in case of transmitting torque lower than the rated one. When under variable loads the tubes are set in vibration which is only partially damped by the elastic silicone resin that interconnects the tubes. As the ship's line shafting does not operate under the rated load at all times, the teeth of the disks set on the inner tubes are liable to heavier wear than those of the disks set on the outer tubes which results in reduced thickness thereof and, consequently, in lower loads taken up by the inner tubes. Variable loads taken up primarily by the inner tubes involve higher margin of safety thereof which precludes uniform load distribution between the inner and outer tubes.
Sophisticated construction of such shafts and necessity for the disks to be welded to the tubes after tooth cutting fails to provide adequate accuracy of the clearances between the teeth of the disks and the clutches, whereas tooth cutting made after welding the disks to the tubes requires unique equipment and fails to provide accurate tooth cutting due to inadequate rigidity of the entire construction.
Furthermore, it is due to the fact that the stressed condition of the tubes is established only when under working load that control over the uniform loading of the tubes proves to be difficult.
The shaft features but low level of repairability as being of inseparable construction.